A MNO provides a wireless voice service and a data communication service (e.g., a call and a message) to a mobile user who is subscribed to the MNO. In order to attract a new subscriber in a competition with other MNOs, an MNO offers a special rate promotion or provides a free phone call and a free message performed between the users subscribed to the same or related MNO. However, it is difficult for a user to determine whether the telephone number in his/her contact list is a telephone number with which a call and a message can be performed with a discounted rate, sometimes there is a restriction in using the discounted rate effectively.